Wooden I-beams and I-joists are increasingly used in the construction industry, as they eliminate many of the problems that occur with conventional wooden joists.
I-joists are made of a web which is sandwiched between two flanges, such that the cross-section of these joists has an I-shape. The flanges are usually made from laminated veneer lumber or solid wood, and are grooved on one side to receive the web. The web is usually made from oriented strand board (OSB), plywood or laminated veneer lumber. The I-joist is assembled by gluing the web to the top and bottom flanges.
The advantage of I-joists is that the web resists shear forces while the flanges resist most types of pressure applied to the beam that can cause bending or breakage. Beam theory shows that the I-shaped form is very efficient for carrying both bending and shear loads in the plane of the web.
Although I-joists offer substantial advantages compared to conventional wood joists, the I-joist can fail if it is incorrectly altered. Constructions often require perforating and cutting holes in the web of the I-joists, so that air ducts, electrical wiring and plumbing pipes can pass through. Typical mistakes made by subcontractors include incorrectly placing or sizing holes in the web. Doing so can greatly compromise the strength of the joist.
In order to prevent this problem, I-joist distributers and wholesalers often use digitally controlled routers (also known as cnc routers) to cut or drill holes in the I-joists at specific locations. Such a system typically consists of a flat horizontal platform equipped with an XYZ grantry system on which a spindle router is mounted. The I-joist is maintained in place on the platform by clamps or by a vacuum. The yield of such systems is clearly limited, as an operator must manually position each individual I-joist on the platform before the router can cut it. Such systems are also limited with regard to the size of the holes they can cut in the web.
The Applicant is also aware of a system known as SawTek in which beams are moved longitudinally using a computer driven trolley. Such system is limited in terms of efficiency and productivity, since the beam must be stopped, and then clamped prior to being cut.
In order to prevent these problems, I-joists could be manufactured with pre-cut holes. The web of such joists could be cut or perforated prior to gluing the top and bottom flanges to it. However, distributers and wholesalers of joists are not inclined to assemble I-joists themselves, because the use of glue would require them to comply with strict environmental, security, performance and health standards.
There is therefore a need for an apparatus and method of perforating beams with increased yield. There is a need for an apparatus and method for perforating openings sized and positioned so that the strength of the beam is preserved. There is also a need for an apparatus and method which allow perforating the body portion or web of beam over their entire transverse height.